1. Field of the Invention
The present invention relates to a method of manufacturing a thin-film magnetic head having at least an induction-type electromagnetic transducer.
2. Description of the Related Art
Recent years have seen significant improvements in the areal recording densities of hard disk drives. In particular, the areal recording densities of latest hard disk drives have reached 100 to 160 gigabytes per platter and are even exceeding that level. It is required to improve the performance of thin-film magnetic heads, accordingly.
Among the thin-film magnetic heads, widely used are composite thin-film magnetic heads made of a layered structure including a recording (write) head having an induction-type electromagnetic transducer for writing and a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading.
Typically, the write head incorporates: a medium facing surface (an air bearing surface) that faces toward a recording medium; a bottom pole layer and a top pole layer that are magnetically coupled to each other and that include magnetic pole portions opposed to each other and located in regions of the pole layers on a side of the medium facing surface; a write gap layer provided between the magnetic pole portions of the top and bottom pole layers; and a thin-film coil at least part of which is disposed between the top and bottom pole layers and insulated from the top and bottom pole layers.
A higher track density on a recording medium is essential to enhancing the recording density among the performances of the write head. To achieve this, it is required to implement the write head of a narrow track structure in which the track width, that is, the width of the two magnetic pole portions opposed to each other with the write gap layer disposed in between, the width being taken in the medium facing surface, is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to achieve the write head having such a structure.
One of the parameters that affect the writing characteristics of the thin-film magnetic head is the throat height. The throat height is the length (height) of the pole portions, that is, the portions of the two pole layers opposed to each other with the write gap layer in between, as taken from the medium-facing-surface-side end to the other end. The throat height affects the intensity and distribution of the magnetic field generated near the write gap layer in the medium facing surface.
Moreover, it is required that the write head have an excellent overwrite property as a parameter indicating an overwriting capability. To improve the overwrite property, it is necessary to introduce as great a part of magnetic flux passing through the two pole layers as possible to the pole portions and to generate a large magnetic field near the write gap layer in the medium facing surface. Therefore, it is effective to increase the thickness of the pole portions and to reduce the throat height for improving the overwrite property.
As disclosed in the U.S. Pat. No. 5,793,578 as prior art, the track width and the throat height are defined by the top pole layer in many of conventional thin-film magnetic heads. In such a case, for example, the insulating layer covering the thin-film coil protrudes upward from the top surface of the write gap layer, and the throat height is defined by one of the ends of this insulating layer closer to the medium facing surface. The top pole layer includes: a track width defining portion that has an end located in the medium facing surface and that defines the track width; and a wide portion that is located farther from the medium facing surface than the track width defining portion and has a width greater than the track width. The top pole layer is formed on the write gap layer and the above-mentioned insulating layer by a method such as frame plating.
The following is a description of a method of forming the top pole layer by frame plating on the write gap layer and the insulating layer that defines the throat height as described above. In this method an electrode film is formed on the write gap layer and the insulating layer that defines the throat height. Next, a photoresist layer is formed on the electrode film. The photoresist layer is made of a positive resist in this case. Next, the photoresist layer is exposed to light having a pattern corresponding to the shape of the top pole layer. The photoresist layer is then developed. A groove corresponding to the shape of the top pole layer is thereby formed in the photoresist layer. This photoresist layer serves as a frame. Next, electroplating is performed, using the frame and feeding a current to the electrode film, to form the top pole layer in the groove.
This method has the following problem. When the photoresist layer is exposed, the light used for exposure is reflected off the electrode film. Here, the surface of the insulating layer that defines the throat height includes a portion near the medium facing surface that forms a sloped surface. As a result, part of light reflected off the electrode film disposed on this sloped surface reaches a portion of the photoresist layer corresponding to the pole portion of the top pole layer. Consequently, the portion of the photoresist layer corresponding to the pole portion of the top pole layer is exposed to not only the light having a pattern corresponding to the pole portion but also the part of light reflected off the electrode film disposed on the sloped surface. It is therefore difficult through the above-described method to form the portion of the frame corresponding to the pole portion of the top pole layer with accuracy. In particular, it is extremely difficult through the method to form the pole portion having a width of 0.05 to 0.15 micrometer (μm) and a sufficient thickness.
To solve this problem, a thin-film magnetic head has been proposed wherein a concave portion is formed in the bottom pole layer and the thin-film coil is placed in the concave portion, and the top pole layer is formed on a flat surface. In this type of head the throat height is defined by an end of the concave portion closer to the medium facing surface. This type of head is disclosed in the U.S. Pat. No. 5,793,578, the U.S. Pat. No. 6,400,525B1 and the U.S. Pat. No. 6,259,583B1, for example. This head allows the pole portion of the top pole layer to be formed with more accuracy, compared to the case in which the top pole layer is formed on the insulating layer that defines the throat height.
However, the case in which the top pole layer is formed by frame plating involves the following problem even though the top pole layer is formed on a flat surface. As described above, the top pole layer has the track width defining portion and the wide portion. To improve the overwrite property, it is desirable that the length of the track width defining portion taken in the direction orthogonal to the medium facing surface is smaller. The wide portion is much greater than the track width defining portion. Therefore, when the photoresist layer is exposed, part of light reflected off the portion of the electrode film corresponding to the wide portion reaches the neighborhood of the portion of the photoresist layer corresponding to the interface between the track width defining portion and the wide portion. As a result, there arises a problem that the neighborhood of the portion of the frame corresponding to this interface loses shape. Since reflected light broadens while travelling, disturbance to the shape of the frame is greater in the upper portion of the frame. Such disturbance to the shape of the frame results in disturbance to the shape of the neighborhood of the interface between the track width defining portion and the wide portion of the top pole layer. In particular, if the track width is small or the length of the track width defining portion taken in the direction orthogonal to the medium facing surface is small, it is difficult to define the track width with accuracy when the top pole layer loses shape as described above.
If the track width is reduced, in particular, it is required to increase the thickness of the track width defining portion to improve the overwrite property. However, since disturbance to the shape of the frame is greater in the upper portion of the frame as described above, the above-mentioned problem caused by the disturbance to the shape of the frame is more serious as the thickness of the track width defining portion is increased.